linux-kernel - Re: [PATCH 2/2] x86-64: seccomp: fix 32/64 syscall hole

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Message-ID: <alpine.LFD.2.00.0902271932520.3111@localhost.localdomain>
Date:	Fri, 27 Feb 2009 19:36:34 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Roland McGrath <roland@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH 2/2] x86-64: seccomp: fix 32/64 syscall hole



On Fri, 27 Feb 2009, Roland McGrath wrote:
> --- a/arch/x86/include/asm/seccomp_64.h
> +++ b/arch/x86/include/asm/seccomp_64.h
> +/*
> + * This indicates we are inside a 32-bit system call (only testable
> + * synchronously by current), whereas TIF_IA32 indicates we are a 32-bit
> + * task.  A 32-bit task can make a 64-bit syscall by ljmp into 64-bit
> + * USER_CS, and a 64-bit task can make a 32-bit syscall by int $0x80.
> + */
> +#define IS_COMPAT_TASK	is_compat_task()
> +
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> +#if defined TIF_32BIT && !defined IS_COMPAT_TASK
> +# define IS_COMPAT_TASK	test_thread_flag(TIF_32BIT)
> +#endif
> +
> +#ifdef IS_COMPAT_TASK

Ok, please explain this madness.

The whole crazy IS_COMPAT_TASK dance seems to be too messy for words. Why? 
What's going on?

		Linus
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